This invention relates to a 2-cycle engine and more particularly to an improved scavenging system for such an engine and to a scavenge pump and pressure relief system.
The advantages of supercharging an internal combustion engine so as to improve its performance are well known. Supercharging has particular advantages with 2-cycle engines because it permits better scavenging of the engine and also permits the intake air charge to be directed into the cylinder without having to pass first through the crankcase for normal compression. The advantage of not having the charge pass through the crankcase is that this insures that lubricant from the crankcase will not be discharged through the exhaust of the engine.
In conjunction with supercharging, however, it is desirable to limit the maximum pressure which is exerted in the combustion chamber by the intake charge. Because most internal combustion engines run over a widely varying speed and load range and in order to achieve adequate pressure at lower speed ranges, the pressure output of the pump at higher engine speeds may be greater than that desirable to insure good engine performance. Therefore, it is desirable to provide some form of pressure relief to insure that the maximum pressure in the induction system does not reach too high a value.
Conventionally, it has been the practice to provide a pressure relief valve directly at the output of the supercharger. However, the pressure at the output of the supercharger may vary cyclically and this can cause the pressure relief valve to open and close at times when pressure relief is not actually necessary.
It is, therefore, a principal object of this invention to provide an improved pressure relief system for a supercharger for an internal combustion engine.
It is a further object of this invention to provide an improved scavenging system for a 2-cycle engine embodying a scavenge pump and pressure relief system for it.
In conjunction with the control of pressure in a supercharged engine, the pressure is normally controlled by dumping excess air into the atmosphere at the outlet of the supercharger. When this is done, however, considerable noise is generated and also the air may be discharged in an area where air discharge may be undesirable for a variety of reasons.
It is, therefore, a still further object of this invention to provide an improved pressure relief valve for a supercharged engine wherein the air discharge from pressure relief will be discharged to an area where noise cannot be generated or the noise generation will be minimized.